We report on the analysis of step fluctuations on a Cu (100) electrode in aqueous electrolyte. From the time dependence of the fluctuations we determine the mass transport involved in the fluctuations as a function of the electrode potential. We obtain a value for the total activation energy of the relevant mass transport. The results are compared to those for Ag electrodes and we give a value for the kink energy on silver in a Cu2+ containing electrolyte. The problem of a possible tip influence on the step fluctuations is also addressed.